<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>弹出框</title>
  <style>
    .bg {
      height: 666px;
      width: 100%;
      font-size: 60px;
      text-align: center;
    }
    .dialog {
      z-index: 999;
      position: fixed;
      top: 0;
      right: 0;
      left: 0;
      background-color: rgba(0, 0, 0, 0.5)
    }
    .dialog .content {
      min-height: 300px;
      width: 600px;
      background-color: #fff;
      border-radius: 5px;
      border: 1px solid #ebeef5;
      box-shadow: 0 2px 12px 0 rgba(0, 0, 0, .1);
      position: absolute;
      top: 50%;
      left: 50%;
      transform: translate(-50%, -50%);
    }
  </style>
</head>
<body>
  <div class="bg">
    页面内容
  </div>
  <div class="dialog">
    <div class="content">
      弹出框
    </div>
  </div>
</body>
</html>